The present invention relates to a conductive element to be surface mounted on a printed circuit board by soldering, for example, so as to ground the printed circuit board to a grounding conductor by pressing its elastically deformable contact part against the grounding conductor, and to the manufacturing method thereof.
Presently, there is a known conductive element to be surface mounted on a printed circuit board to ground the printed circuit board by being pressed against a grounding conductor such as a housing panel. For example, Publication of Japanese Unexamined Patent Application No. 8-287980 discloses a grounding terminal (hereinafter referred to as a conductive element) of this type.
As shown in FIG. 9A, a conductive element P1 of this type is reflow soldered to a conductive pattern P3 on a printed circuit board P2 with solder P4. When the conductive element P1 is pressed against a grounding conductor P5, the printed circuit board P2 is grounded.
The conductive element P1 is formed by bending a narrow, thin metal sheet (a metal strip) to have a base P6 and a contact part P7 therein. One surface of the base P6 is a joining surface P8 to be soldered to the conductive pattern P3 on the printed circuit board P2. The contact part P7 adjoins the base 6 and is bent toward the upper direction.
As the result of load by the grounding conductor P5, the contact part P7 is elastically deformed around the bending area bordering the base 6 and is pressed against the grounding conductor P5 by restoring force caused by the elastic deformation, thereby electrically connecting the printed circuit board P2 and the grounding conductor P5 properly.
Recently, there have been studies of a conductive element in which the above mentioned metal strip and a conductive elastomer are joined integrally by applying a conductive elastomeric adhesive to one surface of the metal strip so as to obtain greater elasticity.
However, manufacturing such a conductive element with a joined conductive elastomer involves the following problem:
The metal strip as a blank for the aforementioned conductive element is typically formed by cutting a large rectangular or square metal sheet into strips. The surfaces of the large metal sheet are generally plated with nickel or the like having great joinability with solder so as to increase solderability.
However, once the large metal sheet as mentioned above is cut, its section (cut surface) P11 naturally provides a non-plated, bare metal, as shown in FIG. 9B.
Accordingly, when the conductive element is soldered, it is difficult for solder to attach the cut surface P11 of the metal strip and solderability of the metal strip is decreased, with the result that the joining strength of the conductive element is decreased.
A solution to this problem is to provide an additional step of plating the cut surface P11, but it is difficult to plate such a narrow part as the cut surface P11. Moreover, this solution leads to an increase of the manufacturing cost as well as the manufacturing steps.
Wherefore, an object of the invention is to provide a conductive element realizing high solderability and a manufacturing method thereof, which overcome the aforementioned problem.
According to one aspect of the invention, there is provided a conductive element to be soldered to a supporting element for ensuring conduction (for example, between a printed circuit board to be joined to and a grounding conductor), the conductive element comprising: a plate-like member formed by pressing a metal wire having a surface plated with a solderabe metal; and a conductive elastomer joined to a pressed surface of the plate-like member.
The method of manufacturing the conductive element comprises the steps of: plating a surface of a metal wire with a solderable metal; pressing the metal wire having a surface plated with a solderable metal from a side direction to form a plate-like member having a pressed surface; and attaching a conductive elastomer to the pressed surface of the plate-like member to form the conductive element.
In the present aspect, a metal wire with a plated surface is pressed to form a thin plate-like member and a conductive elastomer is joined to the pressed surface. Since the metal wire is plated along its whole circumference with a metal having great solderability such as nickel, after the metal wire is pressed, even the narrow sides of the plate-like member (i.e. the sides perpendicular to the pressed surfaces) also have plated surfaces. That is, unlike a conventional metal strip, the present plate-like member does not provide any non-plated surfaces.
Accordingly, when the conductive element is soldered to a printed circuit board, solder is spread over the narrow side surfaces of the plate-like member, and therefore the conductive element and the printed circuit board can be joined firmly.
Also, since separate plating of the conventionally non-plated side surfaces of the plate-like member is not necessary, the whole manufacturing process is simplified and cost reduction is achieved.
It is preferable that the conductive element in the above aspect of the invention has concavities and convexities in the pressed surface of the plate-like member, and that the manufacturing method thereof includes forming the concavities and convexities during the press operation. These concavities and convexities formed, for example, in the axial direction in the pressed surface of the plate-like member, improve joinability with the conductive elastomer.
According to another aspect of the invention, there is provided a conductive element comprising: a plate-like member formed by pressing a bundle of a plurality of metal wires each metal wire having a surface plated with a solderable metal; and a conductive elastomer joined to a pressed surface of the plate-like member.
The method of manufacturing the conductive element comprises the steps of: binding a plurality of metal wires each having a surface plated with a solderable metal; pressing the bound plurality of metal wires from a side direction thereof to form a plate-like member having a pressed surface; and attaching a conductive elastomer to the pressed surface of the plate-like member to form the conductive element.
In the present aspect, since a plurality of metal wires are bound and pressed together, even the narrow sides of the plate-like member have plated surfaces. This improves joining strength when soldered and achieves cost reduction.
Particularly, in the present aspect, a plurality of metal wires which are bound and pressed together necessarily provide irregularity both in the pressed surfaces and in the narrow side surfaces of the plate-like member. This irregularity provides the advantage of improving joinability with conductive elastomers and solderability as well.
According to a further aspect of the invention, there is provided a method of manufacturing a conductive element as in the above aspects of the invention, further comprising the step of mounting the conductive element to a surface of a printed circuit board by soldering in order to ground the printed circuit board to a grounding conductor by contacting an elastically deformable contact part of the conductive element on the grounding conductor.